# ~ Common Emitter Amplifier ~ Transistor rbb Calculator ~

 To be used with a Common Emitter test jig as described Here Boltzmann Constant — k 1.3806x10-23 J/K    [ Joules/Kelvin ] Charge on a single Electron — q 1.6022x10-19 C   [ Coulomb or Amperes/sec ] Measurement device load — RL Ω Parallel with RC assumed a.c. coupled Collector Resistor — RC Ω Load resistor  [ RE & RS assumed = 0 ] Measured Voltage across RC — VRC V     IC = VRC/RC = mA Measured Voltage Gain AVm  [ affected by high rbb and low ro ] Noise Voltage at Collector — VNtot µVrms  Enter Measured value @ IC T & Bn Transistor d.c. current gain — β hFE from data sheets @ IC or measured Device Temperature — T ˚C    Calculation uses  T =  ˚K Measurement Noise Bandwidth — Bn Hz — Is not the –3dB BW see Here Calculated results using the values entered above Voltage Gain neglecting ro — AV V/V = α RC/re Emitter Internal Resistance — re Ω = VT/IC     VT = kT/q = Load resistor including ro — RCm Ω                     RC || RL =  Ω Internal Collector Resistor — ro kΩ              VA = ro • IC =  V Noise at Collector due to IC — VNIC µVrms = √2 q IC Bn  • (RCm–re) Noise at Collector due to RCm — VNRC µVrms = √4 k T Bn RCm Noise at Collector due to rbb µV = √V2Ntot–V2NRC–V2NIC = √V2Nrbb+V2NIB rbb calculated from √V2Nrbb+V2NIB Ω              The –ve result

The value of RC modified by ro [RCm] must be less than the total collector load RC || RL ~ The calculated value of rbb must be positive and the negative result negative for the answer to be plausible ~ NaN [Not a Number] may indicate the measured gain or other inputs are not correct or a non numeric input was entered

See also ~ rbb calculated from data–sheet values   but beware some data–sheet figures may not be in the units you need

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